The present invention relates to a solid golf ball which has exceptional rebound characteristics and flight performance, as well as a good shot feel.
Golf balls can be broadly classified into two categories: solid golf balls, which exhibit exceptional durability and flight distance, and thread-wound golf balls, which exhibit exceptional controllability and shot feel. Solid golf balls comprise a two-piece ball, of which a core is covered by a cover material, and a multi-layer structured golf ball, in which one or more intermediate layers are interposed between the core and cover.
The core of the solid golf balls is formed by a vulcanized molded article of rubber composition. The rubber composition comprises polybutadiene as a base rubber, a metal salt of xcex1,xcex2-unsaturated carboxylic acid and an organic peroxide. The metal salt of xcex1,xcex2-unsaturated carboxylic acid is grafted onto the polybutadiene main chain through the action of the organic peroxide, which serves as a free radical initiator, and functions as a co-crosslinking agent in the rubber composition. Since the vulcanized molded article of the rubber composition forms the three-dimensionally crosslinked structure therein, it is known to impart the core with a suitable degree of hardness and durability, and solid golf balls, in which such cores are employed, with exceptional durability, as well as good rebound characteristics and flight performance.
However, in comparison to conventional thread-wound golf balls, such solid golf balls exhibit a markedly hard shot feel as well as diminished controllability at approach shot. Efforts made to improve the shot feel have included making the core softer by lowering its hardness. The shot feel is improved as a result; however, there is a lowering in rebound characteristics, which does not allow a sufficient flight distance to be obtained. A further test for improving controllability involving softening the cover has been proposed (Japanese Patent Kokai Publication No. 51406/1995). Whereas the spin performance is improved, the rebound characteristics of the cover are degraded, which led to the problem of sufficient ball flight properties not being obtained.
Other attempts to effect a improvement in both the rebound characteristics and shot feel of solid golf balls have been made by compounding conventional core rubber compositions with various organic sulfur compounds (Japanese Patent Kokai Publication No. 244019/1998, Japanese Patent No. 2778229 and Japanese Patent No. 2669051). However, these attempts have still not yielded a golf ball which is satisfactory from the standpoints of both rebound characteristics and shot feel. Moreover, improved shot feel as well as exceptional flight performance have both been increasingly demanded of golf balls.
With the foregoing problems of conventional golf balls in view, it is an object of the present invention to provide a solid golf ball which has exceptional rebound characteristics and flight performance, together with good shot feel.
The inventors of the present invention performed diligent research in an attempt to achieve the aforedescribed object, and as a result perfected the present invention through the discovery that by employing specific organic sulfur compounds, which contain a substituent group having a substituent constant of at least 1.42, with a core rubber composition containing an xcex1,xcex2-unsaturated carboxylic acid or metal salt of same as a co-crosslinking agent, an organic peroxide, a filler etc. with a polybutadiene or other base rubber, a solid golf ball could be obtained which exhibits exceptional rebound characteristics and flight performance, together with good shot feel.
This object as well as other objects and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawings.